This thesis is devoted to the theoretical study of spin-orbit-induced transport in diffusive normal metals and superconductors. The spin-orbit interaction plays a vital role in the aspiring field of spintronics, which aims to utilize the electron spin with the ambition to enable a new generation of efficient and powerful electronic devices. It provides a link between the spin and charge degrees of freedom, couples spin currents of different polarizations, and leads to the dephasing of spin information.
In this thesis, we elucidate the nature of the spin swapping effect, where the spin polarization and the direction of flow are interchanged due to spin-orbit coupling, and demonstrate that an intrinsic analog to the previously predicted extrinsic spin swapping effect can be induced by Rashba spin-orbit coupling in two-dimensional diffusive metals. Unlike its extrinsic counterpart, intrinsic spin swapping is a strong effect and results in a nontrivial relation between the injected spin flow and the spin polarization. Moreover, a long-range spin swapping effect takes place in narrow strips with intrinsic spin-orbit coupling.
Rich and interesting physics emerge when the useful properties of superconductors are combined with spin generation and manipulation. We study in detail spin relaxation due to magnetic impurity scattering and spin-orbit coupling, skew scattering, the side-jump mechanism, and the spin swapping effect. Employing the quasiclassical theory of superconductivity, we derive kinetic equations describing the transport of spin, charge, and energy in diffusive superconductors, and investigate how the various mechanisms are influenced by superconducting correlations. We find that the spin Hall angle is renormalized by the superconducting density of states and that the spin swapping constant is renormalized implicitly through generalized diffusion coefficients.
Additionally, we consider an inverse spin Hall effect occurring due to the interplay between Rashba spin-orbit coupling and Zeeman fields in S|N|S Josephson junctions in thermal equilibrium. This combination induces an effective vector potential in the normal conductor and gives rise to a supercurrent, in analogy to the Meissner effect. Spin-orbit coupling also diminishes the depairing effects of strong Zeeman fields and leads to a long-range propagation of ±1 triplet components on the scale of the spin-orbit precession length, providing a link between the two superconducting terminals.
It is the aim of this thesis to contribute to a fundamental understanding of the physical properties of nanoscaled condensed matter systems, obtain results that may inspire further research, and thereby aid the development of novel and improved technologies in the promising field of spintronics.